Vortex of Activity

So I etched and soldered up the PWM control board for my stir plate prototype, and it works great. I had just enough of the plexiglass weld / solvent to assemble the top half of the box, but it was enough to mount the major components. It’s not 100% complete as I still need to work out how to handle power and need to put the bottom side on the enclosure. I don’t really want to have a hole that the power wire runs into, so I need to get a power jack and the associated plug and include it in the final wiring. As tight as space is for this prototype, it could be challenging.

Building the prototype brought a few issues forward that I hadn’t considered before, so next time I make one of these it should go a little smoother.

ITEM 1: Super-glueing the magnets to the fan is a royal pain in the neck; it is a manic race between taking time to balance the magnets and avoid the glue hardening when they are in the wrong position. The fact that they are strong rare-earth magnets only complicate things because they want to flip and slide all over the place. Glue can actually act as a lubricant (at least until it hardens) and the magnets will tend to shift. That said, super glue can take longer to completely dry than you think (unless it is on your fingers)… Turning the fan on after 30 minutes when the excess glue isn’t completely dry will cause the fan to fling said excess all over the inside of your fan and make a huge mess. Reign in your enthusiasm and leave it to dry overnight.

ITEM 2: Make sure you take the height of the fan, magnet, and spacers into account when building your enclosure (unless you are just using a pre-fab project box). This height should be the maximum height of your PCB for the control circuit – unless you like needlessly taller enclosures. A good technique here is to print out the circuit on paper, cut it size, and figure out how to orient it in the enclosure along with the switch, LED, potentiometer, fan, etc. Also don’t forget your board width once all the components are mounted – things like electrolytic capacitors and jumpers tend to be the ones that contribute most to the height, but an IC socket with the IC in it can too. When totally assembled, things might turn out tighter than you think. Fortunately my stuff fits just fine – I just had to make the enclosure taller than I intended to accomodate the 2″ board size, and would have preferred something closer to 1″.

ITEM 3: Don’t cut excess length off your potentiometer until you’ve got it mounted in the enclosure. You might not leave enough length for your control knob to grab onto. I barely escaped this particular problem, and a fourth trip to Radio Shack for a replacement pot might have sent me over the edge.

I’m sure there were other “lessons” learned, but they aren’t jumping to mind. Now I just need to get a plan together for my friend Brian and build him a stirplate as well. He’s got some 120V components that he’s going to try to use, so the design will be completely different – although we may need to fall back to this approach if we can’t make his work. I did etch up a spare control board just in case 😉